Although recycling has a long history, it is only relatively recently that environmental protection and waste management issues have come to the forefront of both public and political awareness. Plastic recycling has predominately resulted from packaging applications such as packing films while other areas of polymeric waste include: construction, automotive, agriculture and electrical components.
In the production of BOPP films, the use of recycled or reprocessed propylene polymer-based pellets from waste or non-conforming BOPP films back into the core or base layer of said BOPP film is a common practice to reduce costs by replacing a portion of costlier virgin polypropylene material. Generally, the recycled material is similar in composition to the BOPP film it is being used in. This is to help maintain performance properties for the film's particular application and to maintain aesthetic appearance: It is generally desirable to have a film without gross defects such as gels, specks, excessive haze, low gloss, etc.
Some BOPP films can be modified with a skin layer to improve dramatically gas barrier properties. Such materials can either be coextruded or coated. In the case of coating, the skin layer can be applied via in-line coating (i.e. the barrier coating is done prior to transverse direction orientation in a sequential or simultaneous orientation line) or off-line coating (i.e. the barrier coating is done on a separate piece of equipment after the BOPP film is produced). Such high gas barrier materials are usually polar polymers like ethylene vinyl alcohol (EVOH) or polyvinyl alcohol (PVOH). Of particular interest is a polar polymer with exceptional gas barrier properties such as polyhydroxy amine ether (PHAE) which is currently being produced by ICI Packaging Coatings under the trade name “OXYBLOC®.” Such polar polymers when used as skin layers on polypropylene films often require tie resins or high surface treatment to achieve adequate adherence to the propylene-based polymer substrate.
Recycling of PHAE-coated polypropylene films back into new film is difficult because of the inherent incompatibility between polar materials and non-polar materials. The PHAE-coated polypropylene films when recycled as pellets to be used in the core layer of new OPP films cause poor film appearance such as high haze and a preponderance of gels as well as processing issues such as film breaks. This is because the highly polar nature of PHAE does not disperse well and is basically immiscible with the non-polar polypropylene. Thus, the PHAE can form domains within the propylene-based polymer matrix which in turn, manifests itself in the bulk film as high haze, low gloss, and gels. These domains can also be points of high stress which can cause film breakage during transverse orientation.
Thus, the use of PHAE-coated BOPP as a recycled material for cost reduction is impractical. This then results in higher costs and larger amounts of scrap and waste material which must be disposed of.
U.S. Pat. No. 6,589,621 describes the composition of PHAE materials and the use of it in containers and laminate structures. Product literature from Kuraray Evalca of GF-30 compatibilizers for EVOH materials describes the use of these materials to help improve recyclability/reprocessing of EVOH in a polyolefin. Commonly owned U.S. Pat. No. 7,163,727 describes the use of PHAE on polyolefin and polyester substrates. Commonly-owned U.S. Patent Publication No. 2006/0233988 describes the use of PHAE of different resorcinol diglycidyl ether comonomer content on polyolefin and polyester film substrates. Commonly-owned U.S. Patent Publication No. 2007-0031653 describes the use of PHAE on polyolefin substrates using a tie-layer for improved adhesion. However, there is no mention or contemplation of using PHAE-containing scrap material as a recycle component in the above cited references.
This invention seeks to recycle PHAE-containing laminate films in a virgin polymer without loss in property of the films by combining the recycled PHAE-containing film and virgin polymer.